This application is based on and claims priority under 35 U.S.C.xc2xa7119 with respect to Japanese Application No. 2000-097756 filed on Mar. 31, 2000, the entire content of which is incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to air induction systems. More particularly, the present invention pertains to an air induction system having a variable air induction mechanism varying characteristics of the air induction system and a variable volumetric mechanism in order to obtain the dynamic effects of the induction air.
2. Background of the Related Arts
Conventionally known air induction systems supercharge the induction air, improve the charging efficiency to fill the engine combustion chamber with the induction air, and improve the output performance of the engine by utilizing dynamic effects of the induction air supplied to the combustion chamber of the engine. Generally; the dynamic effects of the induction air utilized in the air induction system of the engine includes the inertia effect and the resonance effect. Supercharging effects due to the inertia effect and the resonance effect can be obtained when the engine rpm and the natural frequency of the air induction system are synchronized. The natural frequency is determined by the length and the sectional area of the air intake passage, and the average volume during the air intake period. It is known that the engine rpm and the natural frequency of the air intake system are synchronized by reducing the sectional area of the air intake passage and by expanding the length of the air intake passage at lower engine speed range. The engine rpm and the natural frequency of the air intake system are also synchronized by enlarging the sectional area of the air intake passage and by shortening the length of the air intake passage at higher engine speed. Accordingly, in general, the range of the engine rpm for obtaining the supercharging effects by the dynamic effects of the induction air is broadened by air induction systems provided with mechanisms varying the length of the air intake passage and the volume of plenum.
Japanese Patent Laid-Open Publication No. S60-169627 discloses a variable air induction system utilizing the foregoing effects. The air induction system according to the aforementioned prior art includes an air intake passage having two branch passages diverged at a predetermined diverging portion, an air expanding chamber provided on the downstream side of the branch passages, and a plurality of independent air intake passages for respective cylinders whose order of air induction does not overlap one another. The air induction system according to the aforementioned prior art further includes a first bypass for communicating two air expanding chambers, and a second bypass for communicating two branch passages at a position between the diverging portion and the air expanding chamber. The air induction system according to the aforementioned prior art further includes first and second switching valves for opening and closing the first and second bypasses respectively in accordance with the rpm of the engine. Thus, the air induction system according to the aforementioned prior art is capable of changing the frequency by which the inertia effects and the resonance effects can be obtained by varying the volume of the air expanding chamber and the length of the air intake passage by controlling the opening and closing of the first and second switching valves provided in the branch passages and the air expanding chamber in accordance with the engine rpm.
It is also known that the output performance of the engine at higher speed ranges is improved by expanding the volume of the plenum downstream of the throttle valve provided on the air induction system of the engine. When the engine revolves at high speed, the amount of the induction air required in the combustion chamber is increased. This brings the necessity to supply the induction air in a larger amount than the volume of the air induction system of the engine. As a result, the induction air is introduced from an end of the air induction system exposed to the atmosphere. In a four-cycle engine, for instance, pistons are descended during the intake stroke period and the pistons work in order to intake the induction air to the combustion chamber. Since the induction air is introduced from the end of the air induction system exposed to the atmosphere, the induction air enters a complicatedly structured air induction system structured in order to obtain the inertia effect and the resonant effect. This causes a very large resistance to the induction air. In this case, the work by the pistons is reduced in accordance with the resistance caused by the flow of the induction air and not all work of the pistons is used for intaking the induction air (that is called pumping losses). That is, the power of the pistons is declined. Provided that the volume of the air induction system can be enlarged when the engine is at the high rpm range, the necessary volume of the induction air for combustion can be supplied to the combustion chamber from the air induction system (not from the end of the air induction system exposed to the atmosphere). Thus, the work of piston in order to intake the induction air to the engine can be reduced to supply the larger amount of the induction air to the combustion chamber and to improve the output performance of the engine.
In the aforementioned prior art, the use of a plurality of switching valves is necessary in order to control the communication of the air intake passages and a plurality of the drive means, and control means are necessary for operating the switching valves. Hence, the number of members comprising the switching valve and the drive means is increased as well as the assembling time due to a complicated structure, which increases the manufacturing cost. In addition, it is difficult to arrange all members in a limited space of the engine compartment.
In the aforementioned prior art, the volume of the air induction system cannot be expanded. When the volume of the air induction system downstream of the throttle valve is expanded, another problem arises, i.e., the delay of the response of engine at lower and middle engine speed range. The output of the engine is variably controlled in accordance with the amount of the induction air introduced into the air intake passages by the increase and decrease of the sectional area of the air intake passages caused by the opening and closing of the throttle valve operated in accordance with the operation of throttle pedal. Since the induction air increased by the opening of the throttle valve is first supplied to the combustion chamber of the engine after fulfilling the volume of the air induction system downstream of the throttle valve when the volume of the air intake passage at the downstream of the throttle valve is large, a lag between the operation of the throttle pedal by the vehicle driver and the increase of the engine output is created. The lag makes the driver feel that the engine response is slow.
According to the aforementioned reason, it is favorable that the volume of the air intake passage be increased only at the higher speed range of the engine. However, in order to achieve this goal, another pair of air expanding chambers, switching valves, drive means, and control means are necessary to be provided to the air induction system. The air induction system would also need to have a structure capable of controlling the communication between the air induction system and the additional air expanding chamber. Since the structure according to the foregoing condition is further complicated compared to the aforementioned prior art, it is difficult to achieve the goal.
In light of the foregoing, it is an object of the present invention to provide an air induction system which is capable of improving the performance at broader range of engine speed with low manufacturing cost and simple structure.
To attain the above object, the following technical means is provided with the air induction system of the present invention which includes a plurality of independent air intake passages in communication with respective cylinders of the engine for supplying air thereto, a surge tank connected to the independent air intake passages for supplying the induction air to the air intake passages, an air induction passage having first and second branch passages each exposed to the atmosphere at one end and connected to the surge tank at another end for introducing the induction air into the surge tank, and a volumetric chamber disposed between the branch passages. The air induction system further includes a first switching valve disposed in the surge tank for selectively interrupting and establishing fluid communication between first and second sections of the surge tank, and a second switching valve separating the volumetric chamber from the first and second branch passages for selectively interrupting and establishing fluid communication between the volumetric chamber and the first and second branch passages. The first and second switching valves being operated by a common drive mechanism in accordance with the magnitude of the engine speed.
According to the foregoing technical means, by providing the volumetric chamber between the branch passages, the volume of the air induction system can be varied to improve the output performance of the engine at the higher speed range. Further, by the function of the second switching valve for controlling the communication between the branch passages and the volumetric chamber, the volumetric chamber can be used only when the expansion of the volume of the air intake passage is necessary at a higher engine speed range and not used when the engine response is delayed by the expanded volume of the air intake passages such as at a lower and a middle engine speed range. Accordingly, both the improvement of the engine output performance and an assurance of good response can be achieved. Further more, since the first and the second switching valves can be operated by a common drive means, the number of the switching valves can be increased without increasing the number of drive means and control means. Thus, the manufacturing cost can be reduced and a simple structure can be achieved.
It is favorable that the second switching valve comprises a rotary switching valve formed with two openings in a hollow cylinder and the hollow portion of the rotary switching valve forms the volumetric chamber.
It is further favorable that a first shaft is formed on the first switching valve and is connected to the drive means, a second shaft is formed on the second switching valve, and a transmitting portion is provided between the first and the second shafts for transmitting the rotation force of the drive means while providing phase-contrast between the first and the second shafts. A biasing means opposes the rotational force provided to the second switching valve by the drive means, and a stopper blocks the rotation of the second switching valve from exceeding a predetermined angle of movement. It is favorable that the air induction system of the present invention is structured to have different periods for opening and closing the first and the second switching valves.